The present invention relates to a thin film having a pattern and a process for the preparation thereof. More particularly, the invention relates to a patterned thin film of a high molecular compound modified so as to be able to form a film by Langmuir-Blodgett technique (hereinafter referred to as "LB technique") and a process for preparing a patterned thin film by forming a thin film according to the LB technique and forming a pattern in the film. The patterned thin film is suitable for use in electronic devices, and when the high molecular compound has a precursor structure capable of forming a 5-membered or 6-membered ring, a patterned, heat resistant polymer thin film is obtained.
In the 1930s, it was found by Langmuir and Blodgett that a fatty acid having 16 to 22 carbon atoms could form a monolayer (monomolecular film) on the surface of water and the monolayers could be built up on a substrate to form a multilayer film. In recent years, various studies have been made on the applications of the built-up films, namely Langmuir-Blodgett films (hereinafter referred to as "LB film"). Outline of the studies made hitherto is disclosed in, for instance, Kotai Butsuri 17, No. 12, 45(1982); Thin Solid Films, 68, No. 1 (1980); Thin Solid Films, 99, No. 1.2.3 (1983); Insoluble monolayers at liquid-gas interfaces (G.L. Gains, Interscience Publishers, New York, 1966); and the like.
Conventional LB films of straight-chain saturated fatty acids are poor in heat resistance and mechanical strength and are not suitable for practical uses. In order to improve these defects, it is proposed, for instance, to polymerize films formed from unsaturated fatty acids such as .omega.-tricosenoic acid, .omega.-heptadecenoic acid and .alpha.-octadecylacrylic acid, unsaturated fatty acid esters such as vinyl stearate and octadecyl acrylate, or diacetylene derivatives. However, these films are insufficient in heat resistance, electric property and other properties. It is also known that some hydrophilic group-containing polymers, such as polyacrylic acids, polyvinyl alcohols, polyethyl acrylates and polypeptides, have film-forming properties. However, none of them are suited as a material for LB films, and no investigations have been made on modification of polymers to make usable, in particular, as a material for LB films.
The present inventors made a study in order to provide LB-films having good heat resistance and mechanical strength, and they have already found and reported in Japanese Unexamined Patent Publication Kokai No. 3024/1988 and EP-A-0230539 that a polymer wherein substituent groups for imparting a hydrophobic property are introduced in the recurring units thereof, is capable of forming a film by the LB technique, and that when the polymer has a precursor structure capable of forming a 5-membered or 6-membered ring, a heat resistant ultrathin film of a polymer having a 5-membered or 6-membered structure is obtained by subjecting the LB films of the precursor polymer to a reaction. The proposed polymer can be used with a known compound capable of forming a thin film by the LB technique, and the mixture can also provide a thin film by the LB technique.
In view of effective utilization of the above proposed thin film in the field of electronics, it is desirable that a pattern is formed so that the film is patternwise present only at a desired portion. However, no many proposals have been made on pattern formation of ultrathin films like LB films. The only technique proposed is a pattern formation wherein a film of the above-mentioned .omega.-tricosenoic acid or diacetylene is irradiated patternwise with ultraviolet rays or electron beams to polymerize it, thus giving a negative pattern. The patterned films of these materials are, as stated above, insufficient in heat resistance and electric properties and are not suitable for use in electronic devices.
It is an object of the present invention to provide a patterned thin film suitable for use in electronic devices.
A further object of the present invention is to provide a thin film prepared by the LB technique and having a pattern.
A still further object of the present invention is to provide a patterned thin film having excellent properties such as heat resistance, chemical resistance and mechanical properties, and having a thickness as thin as not more than 10,000 .ANG..
Another object of the present invention is to provide a process for patterning a ultrathin film prepared by the LB technique.
These and other objects of the present invention will become apparent from the description hereinafter.